Inclusion Criteria: 1. Informed Consent 2. Clinical diagnosis of TDT with ≥ 8 documented RBC transfusion events per year on an annualized basis in the 2-years prior to screening 3. Confirmed beta-thalassemia diagnosis by molecular genetic testing 4. Clinically stable and eligible to receive conditioning chemotherapy 5. Able and willing to use an effective method of contraception from the signing of the informed consent and for one year following ST-400 infusion. Exclusion Criteria: 1. Previous history of autologous or allogeneic blood stem cell transplantation or solid organ transplantation 2. Pregnant or breastfeeding female 3. Medical contraindication to mobilization, apheresis, or conditioning 4. Significant liver, lung, heart, or kidney dysfunction 5. Diagnosis of HIV or evidence of active HBV or HCV 6. History of significant bleeding disorder or uncontrolled seizures 7. History of active malignancy in past 5 years (non-melanoma skin cancer or cervical cancer in situ permitted) any history of hematologic malignancy, or family history of cancer predisposition syndrome without negative testing result in the study candidate. 8. Currently participating in another clinical trial using an investigational study medication, or recent participation in such a trial 9. Previous treatment with gene therapy